Question 1002027
Two bases are here called "widths".  One base is some x and the other width base is 4x.


Initial area is  {{{((4x+x)/2)*12=90}}}
{{{5x(6)=90}}}
{{{30x=90}}}
{{{highlight(x=3)}}}


Triple the area keeping the same two bases' measures.
d is for variable depth.
{{{3*90=270}}}, the tripled area.
-
{{{((4*3+3)/2)*d=270}}}
{{{(15/2)d=270}}}
{{{d=270(2/15)}}}
{{{highlight(d=36)}}}-----the new depth.